This invention relates to transmissions of the toroidal-race rolling-traction type, and more particularly to the variator, that is to say the ratio-varying component, of such a transmission.
As is well known to the man in the art, the essential components of such a variator include at least one input disc and one output disc, rotatable about a common axis so that a pair of discs, one of each type, face each other across an axial clearance. A part-toroidal race is formed in each input disc and another in each output disc, the two races of each disc conforming to different parts of the surface of a single, imaginary torus coaxial with the two discs. A set of variably-oriented rollers rolls in contact with both races, and an "end load" is applied axially to discs to urge the discs and rollers into contact and so enable each roller to transmit the appropriate traction from its input disc to its output disc. By changing the orientation of the rollers, so that the radius at which each roller contacts the input disc changes in the opposite sense to the radius at which contact is made with the output disc, the speed ratio transmitted between the input and output discs is varied also.
In a common known type of such a transmission, of which examples are shown in GB-C-2023753 and U.S. Pat. No. 4,662,248, a single and double-faced output disc lies between two input discs, the toroidal races of which face towards each other. One set of rollers transmits traction between the first input disc and one face of the output disc, and a matching set of rollers transmits traction between the second input disc and the other face of the output disc. In both cases , all the traction is transmitted through a single disc--in these examples, the output disc. This is still the case even if, as has been proposed, the design is inverted so that the two connected output discs lie to either side of a single input disc. It should also be noted that in such a transmission the axially-outermost discs will be of the same kind--that is to say both input or both output--and will therefore be without relative rotation. By avoiding the need for rotary thrust bearings, this greatly simplifies the task of applying to those discs the axial "end load" that has already been mentioned.
A problem that has faced the designers of such variators is that the required traction-transmitting capacity of the variator has dictated the size of the single disc just referred to. If a given variator has to be redesigned to increase its capacity, then that redesign must involve providing a disc that is of greater radius or otherwise of greater strength and size.
The present invention arises from appreciating the possibility of making a variator of higher-than-normal traction-transmitting capacity from discs of only normal size, by providing a coaxial sequence of at least two input discs and at least two output discs arranged in a particular way, which includes the characteristic that all the discs except the first and the last in the sequence are formed with part-toroidal races on both of their faces. The invention is thus distinguished from the known type of variator shown by way of example in FIG. 3 of patent specification EP-A-0306272 in which the output discs 26 and 27, like the input discs 21 and 22, are and can only be single-faced. The invention is defined by the claims, the. contents of which should be read as included within the specification.